Persistent (chronic) viral infections of humans afflict more than 500 million people. A diminished role for dendritic cell (DC) function in generating antiviral T and B lymphocytes, coupled with a functional loss (exhaustion, hyporesponsiveness) in antiviral T cells observed in persistent infections results in the inability of the host to remoe infected cells the factories harboring and producing virus. Although each virus has its own unique signature, the premiere experimental model for study, analysis and obtaining strategies to control persistent viral infections is lymphocytic choriomeningitis virus (LCMV) infection in it murine host. Use of this in vivo model provided the initial evidence that generation of negative regulators of the immune response like IL-10 and PD-1 that were responsible for suppressing the antiviral immune response leading to T cell exhaustion, events that were later and quickly extended to persistent human viral infections like HIV, HCV, and HBV. Our laboratory, with funds from this grant, provided the evidence for IL-10 and its production by DCs. IL- 10 is a key player in the establishment and maintenance of viral persistence as antibody neutralization of IL-10 receptor in vivo restores T cell function leading to purging of virus and elimination of the persistent infection. Utilizing reverse genetics we documented that only two amino acids in the LCMV variant Clone 13 decided if a persistent infection would occur in immunocompetent adult hosts compared to the original cloned LCMV source ARM 53b that does not persist. In the viral spike glycoprotein residue 260 (Cl 13/ARM: leu/phe) determines virus binding to its receptor, alpha-dystroglycan (-DG) which is prominently displayed on DCs and is essential for viral entry. The second mutation in the polymerase gene (residue 1079 Cl 13/ARM: glu/lys) favors a 1.5 to 2 log higher replication in DCs, but not fibroblasts or other cells for LCMV possessing the Cl 13 polymerase gene. This grant proposes to uncover the molecular basis of how virus alters DC function and define how IL-10 causes persistence. Further, the grant also explores the exciting prospect of discovery and utilizing small molecule(s) that block both IL-10 and PD-1 as well as other negative regulators of the immune system induced by persisting viruses. We approach the problem of persistent infection by understanding the molecular and biologic mechanisms underlying virus/DC interactions and T cell exhaustion using the wealth of information, reagents and viruses we and others have generated. We plan to assay for potent, specific small molecules that can reverse the suppression of the virus-specific T cell response caused by both IL-10 and PD-1 thereby restoring antiviral immunity. We hypothesize that therapies for the treatment of viral persistence will result from the basic mechanistic and chemical discovery efforts currently underway. This proposal provides an integrated, multidisciplinary approach to evaluate the role of the virus, immune response and DC that already has proven its capabilities by defining novel mechanisms in viral pathogenesis and persistent viral infections.